The addition of rotator interval closure after arthroscopic repair of either anterior or posterior shoulder instability: effect on glenohumeral translation and range of motion.

BACKGROUND: Although the use of rotator interval closure is frequently advocated as a useful supplement to shoulder instability repairs, the addition of a rotator interval closure after arthroscopic instability repair has not been fully investigated.

PURPOSE: The objective of this study was to investigate whether a rotator interval closure improves glenohumeral stability in an anterior and posterior instability shoulder model.

STUDY DESIGN: Controlled laboratory study.

METHODS: Fourteen fresh-frozen cadaveric shoulder specimens were dissected free of soft tissues, leaving the rotator cuff intact with simulated cuff loading. All specimens were mounted in a custom testing apparatus using infrared sensors to document glenohumeral translation and rotation. The specimens were then tested for stability in the following order: vented/subluxated state, after arthroscopic anterior (Group 1; 7 specimens) or posterior (Group 2; 7 specimens) instability repair with suture anchors, and then after rotator interval closure. For each of the 3 testing conditions, the following were measured: (1) external and internal rotation at neutral, (2) external and internal rotation at 90 degrees of abduction, (3) posterior and anterior translation at neutral rotation (15 N and 25 N), (4) anterior translation at 90 degrees of abduction and external rotation (Group 1; 15 N and 25 N), (5) posterior translation at 90 degrees of flexion and internal rotation (Group 2; 15 N and 25 N), and (6) sulcus testing in neutral (7.5 N).

RESULTS: Posterior stability was only improved after anchor capsulolabral repair (8.0 to 5.0 mm; P = .017, 25 N), but there was no improvement after rotator interval closure (5.0 to 4.6 mm; P = .453). However, anterior stability was improved after capsulolabral repair (8.6 to 4.0 mm; P = .016, 25 N) and also improved further by rotator interval closure (4.0 to 2.4 mm; P = .007). The mean loss of external rotation was significantly increased by the addition of the rotator interval closure in both neutral and abducted glenohumeral positions, with a mean external rotation loss of 28 degrees in neutral (P = .013). The addition of a rotator interval closure did not improve sulcus stability (P = .4).

CONCLUSION: The addition of an arthroscopic rotator interval closure after posterior capsulolabral repair did not improve posterior stability; however, anterior stability was improved further after a rotator interval closure. Inferior stability was not improved. Arthroscopic rotator interval closure significantly decreased external rotation at both neutral and abducted arm positions.

CLINICAL RELEVANCE: Arthroscopic closure may be beneficial in certain cases of anterior shoulder instability; however, posterior instability was not improved. Predictable losses of external rotation after rotator interval closure are of concern.